A scanning electron microscope (SEM) used for the observation, inspection, and measurement of a sample using an electron beam accelerates electrons emitted from an electron source, and focuses and applies the electrons on the sample surface using an electrostatic or magnetic lens. The electrons are referred to as primary electrons. The incident primary electrons cause secondary electrons to be emitted from the sample. In some cases, low-energy electrons are referred to as secondary electrons, and high-energy electrons are referred to as reflection electrons. The secondary electrons are detected while an electron beam is being deflected and scanned. Thus, scanned images of fine patterns on the sample and the composition distribution of the sample can be obtained. Electrons absorbed to the sample are detected, allowing absorption electric current images to be formed as well.
One of basic functions of the scanning electron microscope is the resolution of the electron beam. Various methods are attempted in order to improve the resolution of the electron beam. One of the methods is a technique that reduces the energy distribution of the electron beam using an energy filter. This is a technique in which energy distribution is reduced to decrease chromatic aberration, improving resolution. The energy filter has a trajectory dispersion unit that disperses the trajectory of an electron beam of electrons with a different energy value and a selection slit that selects the energy range of the dispersed electron beam, implementing a reduction in energy distribution. The energy filter is sorted into methods, such as an Ω-filter and a Wien-filter, depending on methods of dispersing the trajectory of electrons.
In order to correctly obtain the effect of the energy filter, it is necessary to apply an electron beam in a desired shape to a desired location on a slit. In order to achieve this, Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2002-524818 (Patent Literature 1), for example, describes a method of measuring the intensity of an electron beam on a plate including a selection slit. Japanese Unexamined Patent Application Publication No. 2011-129257 (Patent Literature 2) describes a method in which an electric current (a slit current) carried through an energy selection slit is minimized, optimizing the position of an electron beam on the energy selection slit. Japanese Unexamined Patent Application Publication No. 2005-294128 (Patent Literature 3) discloses a mechanical slit moving mechanism for selecting a select.